Asphalt-based double-salt template porous carbon electrode material and preparation method and application thereof

Abstract

The application discloses a pitch-based double-salt template porous carbon electrode material and a preparation method and application thereof, and relates to the technical field of porous carbon electrode materials. The preparation method comprises the following steps in sequence: pitch is added into concentrated nitric acid and stirred to react, and after washing, a nitrated product is obtained; the nitrated product, active organic potassium salt and inert inorganic carbonate are uniformly mixed and ground by ball milling, and then pre-oxidation and carbonization treatment are carried out, and washing is performed until neutral, so that the pitch-based double-salt template porous carbon electrode material is obtained. The application further discloses the pitch-based double-salt template porous carbon electrode material and application thereof in removal of nitrate and ammonia nitrogen in water by a capacitive deionization technology. The application constructs a large-mesopore-micropore coordinated multi-level pore structure in a pitch carbon skeleton through a double-salt template, realizes efficient adsorption of two kinds of nitrogen pollutants, i.e. nitrate and ammonia nitrogen, and has important practical application value.

Description

Technical Field

[0001] This invention relates to the field of porous carbon electrode materials technology, specifically to a pitch-based dual-salt template porous carbon electrode material, its preparation method, and its application. Background Technology

[0002] Ammonia nitrogen (NH4) + ) and nitrate (NO3) - Nitrogenous pollutants are the most typical nitrogenous pollutants in urban sewage, industrial wastewater, and agricultural runoff. Excessive discharge can cause eutrophication, algal blooms, and deterioration of benthic environments, threatening drinking water safety and human health. Although existing biological denitrification, ion exchange, and reverse osmosis processes are widely used, they generally suffer from problems such as complex processes, high energy consumption, susceptibility to secondary pollution, and sensitivity to fluctuations in influent water quality, making it difficult to simultaneously achieve high efficiency, energy conservation, and sustainability.

[0003] Capacitive deionization (CDI), as an emerging water treatment technology, relies on an electro-bilayer physical adsorption mechanism to achieve reversible desalination and pollutant removal at relatively low voltages. It offers advantages such as low energy consumption, process controllability, and ease of modularization. Electrode materials are the core of CDI technology; their pore structure, specific surface area, and surface functional groups directly determine the ion transport rate and adsorption capacity. Currently, activated carbon, activated carbon fiber (ACF), carbon aerogel, and graphene-based materials are widely used, but most applications still revolve around simple electrolytes such as NaCl, with limited application targeting NH4+. + / NO3 - Systematic research and dedicated electrode materials for the synergistic removal of nitrogen pollutants remain limited.

[0004] Asphalt resources are widely available, low in cost, and high in carbon content, making them an excellent precursor for the preparation of porous carbon electrodes. Traditional strong base activation processes such as KOH and NaOH can significantly increase the specific surface area, but they suffer from problems such as strong corrosivity, heavy post-processing burden, and poor controllability of pore structure. In recent years, salt template pore-forming strategies have been used to construct asphalt-based porous carbon, which can improve ion transport channels to some extent. However, existing studies mostly use single salt templates, which still have shortcomings in controlling macro / meso / micropores.

[0005] Therefore, there is an urgent need to develop a method based on inexpensive asphalt precursors, which combines porous structure and surface function regulation, and is suitable for NH4. + and NO3 - High-performance CDI electrode materials with synergistic removal. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a pitch-based dual-salt template porous carbon electrode material, its preparation method, and its application. The present invention constructs a hierarchical porous structure with macro-meso-micropore synergy in the pitch carbon skeleton through a dual-salt template, achieving efficient adsorption of two nitrogen pollutants, nitrate and ammonia, which has significant practical application value.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a pitch-based dual-salt template porous carbon electrode material is provided, comprising the following steps:

[0008] (1) Add asphalt to concentrated nitric acid and stir to react. After washing, the nitration product is obtained.

[0009] (2) The nitration product, active organic potassium salt and inert inorganic carbonate obtained in step (1) are mixed evenly and ground by ball milling. Then, the mixture is heated to 300-350℃ under nitrogen atmosphere for pre-oxidation, and then heated to 780-820℃ for carbonization. The mixture is washed until neutral to obtain asphalt-based dual salt template porous carbon electrode material.

[0010] Concentrated nitric acid refers to a nitric acid solution with a mass concentration of not less than 68%.

[0011] Asphalt can be made from coal tar pitch, petroleum pitch, coal tar pitch, bio-asphalt, or asphalt materials modified by oxidation / hydrogenation.

[0012] Furthermore, in step (1), the mass-to-volume ratio of asphalt to concentrated nitric acid is 15-25 g: 100 mL.

[0013] Furthermore, in step (1), the reaction is stirred at 70-90℃ for 8-12 h.

[0014] Furthermore, in step (2), the active organic potassium salt is at least one of potassium benzoate, potassium citrate, and potassium oxalate.

[0015] Furthermore, in step (2), the active organic potassium salt can be replaced with other aromatic potassium salts.

[0016] Furthermore, in step (2), the inert inorganic carbonate is at least one of sodium carbonate and sodium bicarbonate.

[0017] Furthermore, the mass ratio of asphalt, active organic potassium salt, and inert inorganic carbonate is 2:2-6:2-4.

[0018] Furthermore, in step (2), the heating rate is 4-6 ℃ / min.

[0019] Furthermore, in step (2), the pre-oxidation time is 1.5-2.5 h; the carbonization time is 1.5-2.5 h.

[0020] Furthermore, after mixing the components in step (2), nitrogen- or sulfur-containing small molecules (such as urea, melamine, thiourea, etc.) can be introduced for N or S doping to improve the electrode's hydrophilicity, pseudocapacitive contribution, and resistance to NO3. - / NH4 + Its specific adsorption capacity.

[0021] The present invention also provides a pitch-based dual-salt template porous carbon electrode material, characterized in that it is prepared by the above-described preparation method.

[0022] The present invention also provides the application of the above-mentioned pitch-based dual-salt template porous carbon electrode material, which is used to remove nitrate and ammonia nitrogen from water through capacitive deionization technology.

[0023] The present invention also provides the application of the above-mentioned pitch-based dual-salt template porous carbon electrode material, which is used to prepare a capacitor deionization device.

[0024] Furthermore, the aforementioned pitch-based dual-salt template porous carbon electrode material can be applied to the preparation of various device structures such as symmetric CDI, membrane capacitor deionization (MCDI), and asymmetric CDI.

[0025] The present invention has the following beneficial effects:

[0026] 1. In the preparation method of this invention, a dual-salt template is used, and an active organic potassium salt provides K. + The activation effect of NO3- and carbonate vaporization etching have a synergistic effect, forming a hierarchical porous structure with macro-meso-micropore synergy in the pitch carbon skeleton. This significantly reduces the diffusion resistance from the solution to the active sites and enhances NO3- concentration. - / NH4 + The mass transfer rate.

[0027] 2. The material of this invention possesses both a high specific surface area and a reasonable pore size distribution. The micropores provide a high ion storage capacity in the electrically double layer, while the mesopores / macropores provide rapid mass transfer channels, achieving a balance between high adsorption capacity and high kinetic performance. Simultaneously, the hierarchical pore structure and relatively complete carbon framework help construct a continuous conductive network, reducing charge transfer impedance and diffusion impedance. This allows the CDI system to achieve high removal efficiency at lower voltages and maintain a high capacity retention rate even after multiple adsorption-desorption cycles.

[0028] 3. By adjusting the ratio of the two salts and the carbonization conditions, this invention can obtain a surface chemical environment containing appropriate amounts of oxygen- and nitrogen-containing functional groups, thereby achieving synergistic and efficient removal of two nitrogen pollutants in the same CDI unit.

[0029] 4. This invention uses relatively inexpensive and less corrosive salts such as potassium benzoate and sodium carbonate to replace traditional strong corrosive activators such as KOH, which can significantly reduce reagent consumption and post-treatment difficulty, alleviate equipment corrosion and waste liquid treatment pressure, and is more conducive to large-scale and engineering promotion. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the CDI device manufacturing process;

[0031] Figure 2 This is a schematic diagram of the testing device;

[0032] Figure 3 CV curves for different porous carbon electrode materials;

[0033] Figure 4 GCD curves for different porous carbon electrode materials;

[0034] Figure 5 Figure 1 shows the adsorption capacity test results for different porous carbon electrode materials.

[0035] Figure 6 The figure shows the effect of working voltage on the adsorption performance of porous carbon electrode materials.

[0036] Figure 7 The figure shows the effect of feed concentration on the adsorption performance of porous carbon electrode materials. Detailed Implementation

[0037] The principles and features of this invention are described below. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0038] Example 1

[0039] A pitch-based dual-salt template porous carbon electrode material is prepared by the following steps:

[0040] (1) Coal tar pitch was added to concentrated nitric acid and stirred at 80°C for 10 h. After washing, the nitration product was obtained. The mass-volume ratio of pitch to concentrated nitric acid was 20 g: 100 mL.

[0041] (2) The nitration product obtained in step (1), potassium benzoate and sodium carbonate are mixed evenly and ground by ball milling. Then, under a nitrogen atmosphere, the mixture is heated to 300℃ for 2 h at a heating rate of 5 ℃ / min and then carbonized at 800℃ for 2 h at the same heating rate. The mixture is washed until neutral to obtain asphalt-based double salt template porous carbon electrode material.

[0042] The mass ratio of asphalt, potassium benzoate, and sodium carbonate is 2:3:2.

[0043] Example 2

[0044] A pitch-based dual-salt template porous carbon electrode material is prepared by the following steps:

[0045] (1) Coal tar pitch was added to concentrated nitric acid and stirred at 70°C for 8 h. After washing, the nitration product was obtained. The mass-volume ratio of pitch to concentrated nitric acid was 15 g: 100 mL.

[0046] (2) The nitration product obtained in step (1), potassium citrate and sodium carbonate are mixed evenly and ground by ball milling. Then, under a nitrogen atmosphere, the mixture is heated to 320°C for 1.5 h at a heating rate of 4 °C / min and then carbonized at 780°C for 1.5 h at the same heating rate. The mixture is washed until neutral to obtain asphalt-based double salt template porous carbon electrode material.

[0047] The mass ratio of asphalt, potassium citrate, and sodium carbonate is 2:2:2.

[0048] Example 3

[0049] A pitch-based dual-salt template porous carbon electrode material is prepared by the following steps:

[0050] (1) Coal tar pitch was added to concentrated nitric acid and stirred at 90°C for 12 h. After washing, the nitration product was obtained. The mass-volume ratio of pitch to concentrated nitric acid was 25 g: 100 mL.

[0051] (2) The nitration product obtained in step (1), potassium oxalate and sodium bicarbonate are mixed evenly and ground by ball milling. Then, under a nitrogen atmosphere, the mixture is heated to 350°C for 2.5 h at a heating rate of 6 °C / min and then carbonized at 820°C for 2.5 h at the same heating rate. The mixture is washed until neutral to obtain asphalt-based double salt template porous carbon electrode material.

[0052] The mass ratio of asphalt, potassium oxalate, and sodium bicarbonate is 2:6:4.

[0053] Comparative Example 1

[0054] A pitch-based porous carbon electrode material (C) is prepared by the following steps:

[0055] (1) Coal tar pitch was added to concentrated nitric acid and stirred at 80°C for 10 h. After washing, the nitration product was obtained. The mass-volume ratio of pitch to concentrated nitric acid was 20 g: 100 mL.

[0056] (2) The nitration product obtained in step (1) is heated to 800℃ for 2 h under nitrogen atmosphere at a heating rate of 5 ℃ / min, and washed until neutral to obtain asphalt-based porous carbon electrode material.

[0057] Comparative Example 2

[0058] A pitch-based porous carbon electrode material (PCTP-2) is prepared in a way that differs from that in Example 1, potassium benzoate and sodium carbonate are not added in step (2), but potassium citrate is added; the mass ratio of pitch to potassium citrate is 2:2.

[0059] Comparative Example 3

[0060] A pitch-based porous carbon electrode material (PCTP-4) is prepared in a way that differs from that in Example 1, potassium benzoate and sodium carbonate are not added in step (2), but potassium citrate is added; the mass ratio of pitch to potassium citrate is 2:4.

[0061] Comparative Example 4

[0062] A pitch-based porous carbon electrode material (HPCM-1) is prepared in a way that differs from that in Example 1, potassium benzoate and sodium carbonate are not added in step (2), but calcium carbonate and sodium chloride are added; the mass ratio of pitch, calcium carbonate and sodium chloride is 2:3:2.

[0063] Experimental Example 1

[0064] The porous carbon electrode materials of Example 1 and Comparative Examples 2-4 were used as electrodes in the CDI device. A schematic diagram of the device fabrication process is shown below. Figure 1 As shown, at 1.2 V, 200 mg L -1 NO3 - / NH4 + When running in solution, its adsorption capacity is tested (see schematic diagram of the testing device). Figure 2 (As shown in the figure), the results are shown in Table 1.

[0065] Table 1. Adsorption capacity test results of different porous carbon electrode materials

[0066]

[0067] As shown in the table, the adsorption capacity of pitch-based porous carbon (PCTP series) prepared using potassium citrate single-salt soft template is limited, with a maximum adsorption capacity of 500 mg. L -1 The deionization capacity of a capacitor under 1.2 V voltage conditions is typically 13.0-18.3 mg. g -1(PCTP-2 and PCTP-4); HPCM-1 porous carbon prepared using CaCO3 / NaCl hard templates, at an initial concentration of 500 mg L -1 The adsorption capacity at 1.2V is mg. g -1 Most of the aforementioned single-salt template materials are only suitable for a single ion and can only achieve a moderate level of desalination capacity at higher influent concentrations.

[0068] In contrast, this invention employs a potassium benzoate-sodium carbonate dual-salt synergistic template modification of asphalt, combining soft template vaporization with inorganic salt gas etching to construct an NC-K3-Na porous carbon electrode with high specific surface area and interconnected hierarchical channels in a one-step heat treatment process. This is achieved with only 200 mg of [material / material - likely a specific material or process]. L -1 In a NaNO3 solution, NO3- of NC-K3-Na - The adsorption capacity can reach 25.96 mg·g. -1 The solution concentration was significantly lower than that in existing literature (500 mg·L⁻¹). -1 Under these conditions, it is still higher than HPCM-1 at 500 mg·L⁻¹. -1 22.0 mg·g of NaNO3 -1 More importantly, at the same voltage and initial concentration (200 mg·L⁻¹), - 1 Under NH4Cl, the material of the present invention is effective against NH4. + The adsorption capacity can also reach 19.17 mg·g. -1 NO3 was achieved - and NH4 + Simultaneous and efficient removal of dual nitrogen pollution is required, whereas existing single-salt template pitch-based carbon materials typically only target the removal of single anions or cations, making it difficult to achieve both simultaneously.

[0069] As can be seen, the dual-salt template hierarchical porous carbon electrode of the present invention has the ability to control NO3 under low concentration conditions. - Removal capacity, and simultaneous removal of NO3 - and NH4 + Its comprehensive processing capabilities still show a clear advantage, fully demonstrating the technological advancements of dual-salt synergistic templates in pore structure optimization and capacitive deionization performance improvement.

[0070] Experimental Example 2

[0071] Referring to the preparation method in Example 1, different porous carbon electrode materials were prepared by adjusting the ratio of asphalt, potassium benzoate, and sodium carbonate to 2:2:2, 2:3:2, 2:4:2, and 2:6:4, respectively, and labeled as NC-K. X-Na (where X represents the amount of potassium benzoate added, taking values ​​of 2, 3, 4, and 6), and test its performance.

[0072] (1) The specific surface area and pore structure test results of different porous carbon electrode materials are shown in Table 2.

[0073] Table 2. Results of Specific Surface Area and Pore Structure Tests

[0074]

[0075] As shown in Table 2, compared with sample C, the specific surface area and pore volume of the samples modified by salt template increased. Among them, NC-K3-Na had the highest specific surface area and the largest pore volume.

[0076] (2) The CV curves and GCD curves of different porous carbon electrode materials are shown below. Figure 3 and Figure 4 As shown in the figure. The results show that, compared with sample C, the specific capacitance of the samples modified by salt template is increased, confirming that salt template modification can effectively improve the charge transfer and ion diffusion capabilities of electrode materials.

[0077] (3) At an initial concentration of 200 mg / L -1 Adsorption experiments were conducted on different porous carbon electrode materials under a voltage of 1.2 V. The adsorption capacity test results are as follows: Figure 5 As shown.

[0078] Depend on Figure 5 It can be seen that, compared with sample C, the modified electrode material has better resistance to NO3. - and NH4 + The adsorption performance of all ions was significantly enhanced, demonstrating the potential to simultaneously remove nitrogen pollutants. For the modified material, the adsorption capacity of the electrode material showed a trend of first increasing and then decreasing with increasing potassium benzoate content. This is mainly attributed to the fact that, under a suitable salt-template ratio, K... + The synergistic effect between vapor etching and sodium carbonate activation significantly improves the adsorption performance of electrode materials. In contrast, excessive salt template activation leads to partial collapse of the pore structure in the electrode material, resulting in a decrease in adsorption performance. Among these, NC-K3-Na exhibits the best adsorption performance.

[0079] (4) Using the NC-K3-Na sample, the effect of the working voltage (0.8-1.4 V) on the adsorption performance of the electrode material was further tested (other key parameters were kept consistent, such as voltage and flow rate). The results are as follows: Figure 6 As shown.

[0080] Experiments show that as the operating voltage increases from 0.8 V to 1.4 V, NO3... - and NH4+ The adsorption capacities of all samples continued to increase, reaching approximately 31.00 mg g at 1.4 V. -1 and 23.10 mg g -1 This is mainly because the increased voltage enhances the electrode polarization and the electric field effect within the pores, promoting ion migration and thus improving adsorption performance. However, according to experimental results, we found that a working voltage of 1.4 V inevitably leads to some side reactions (such as water electrolysis) during CDI adsorption, increasing energy consumption and causing oxidation and deterioration of the electrode material surface. Therefore, a voltage of 1.2 V is more conducive to ensuring efficient and stable adsorption of CDI.

[0081] (5) Further testing was conducted using NC-K3-Na samples at different feed concentrations (50-500 mg / L). -1 The effect of this on the adsorption performance of the electrode material (while keeping other key parameters such as voltage and flow rate consistent) is shown in the following results. Figure 7 As shown.

[0082] Experimental results show that when the feed concentration is increased from 50 mg / L... -1 Increase to 500 mg L -1 At the same time, the adsorption capacity of both ions showed an increasing trend. This is mainly because the increased concentration not only enhances the driving force of mass transfer and the electrochemical potential gradient, but also accelerates the migration process of ions to the electrode surface, while increasing the occupancy rate of active sites in the electric double layer, thereby significantly enhancing the adsorption effect.

[0083] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a pitch-based dual-salt template porous carbon electrode material, characterized in that, The steps are as follows: (1) Add asphalt to concentrated nitric acid and stir at 70-90℃ for 8-12 h. After washing, the nitration product is obtained. The mass-volume ratio of asphalt to concentrated nitric acid is 15-25 g: 100 mL. (2) The nitration product, active organic potassium salt and inert inorganic carbonate obtained in step (1) are mixed evenly and ground by ball milling. Then, the mixture is heated to 300-350℃ under nitrogen atmosphere for pre-oxidation, and then heated to 780-820℃ for carbonization. The mixture is washed until neutral to obtain asphalt-based dual-salt template porous carbon electrode material. The mass ratio of the asphalt, active organic potassium salt and inert inorganic carbonate is 2:2-6:2-4. The pre-oxidation time is 1.5-2.5 h. The carbonization time is 1.5-2.5 h. The active organic potassium salt is potassium benzoate. The inert inorganic carbonate is sodium carbonate.

2. A pitch-based dual-salt template porous carbon electrode material, characterized in that, It was prepared using the method for preparing pitch-based dual-salt template porous carbon electrode material as described in claim 1.

3. The application of the pitch-based dual-salt template porous carbon electrode material according to claim 2, characterized in that, The asphalt-based dual-salt template porous carbon electrode material is used to remove nitrate and ammonia nitrogen from water using capacitive deionization technology.

4. The application of the pitch-based dual-salt template porous carbon electrode material according to claim 3, characterized in that, The asphalt-based dual-salt template porous carbon electrode material is used to prepare a capacitor deionization device.

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